1. Field of the Invention
The invention relates to a packing bag which has drawstrings, and more particularly relates to a packing bag having one or more drawstrings which are inserted in a sleeve formed around and along an open top end of a main body of the packing bag, wherein the drawstrings are capable of being pulled in opposite directions respectively at their opposite side ends so that an upper portion of the packing bag is gathered to close the open top end.
2. Description of Prior Art
In such a conventional type of packing bag as shown in FIG. 15, upper portions of a bag's flat main body 51 made of a thermoplastic resin film are folded over such that the upper portions' extremities are thermally welded respectively to a front and back walls 52 and 52 of the packing bag's main body 51. A front and back sleeves 53 and 53 for accommodating drawstrings are formed in this manner to extend around an open top end of the bag. An upper and lower drawstrings 54 and 54 inserted in each sleeve 53 will be tightened to close the open top end (see for example Japanese Patent Publication Hei. 1-32170 and Japanese Utility Model Publication Sho 50-8087). An end of one drawstring 54 and an opposite end of the other drawstring 54 are pulled in opposite directions to gather the upper portions so as to close the bag as shown in FIG. 16.
It is however to be noted that the tightened ends of the drawstrings 54 are likely to slacken while the bag is suspended from a user's hand and carried by him, or when the drawstrings are knotted one with the other. As a result, the binding force of the drawstrings 54 becomes so weak that the resiliency of the resin film will loosen the tightly gathered top end to open.